Clinical and necropsy observations are described in 61 patients in whom one or more cardiac valves had been replaced with discoid prostheses (Hufnagel type). The disc-poppet prosthesis is not an ideal substitute cardiac valve. It clots, despite anticoagulant therapy, it is intrinsically stenotic, protions of it, i.e., the disc, degenerate, and it causes hemolysis to erythrocytes.